This invention relates to a multichip module, and more particularly to a cooling structure cooling a multichip module for effectively removing heat generated from integrated circuit chips.
In for example U.S. application Ser. Nos. 604,003 now U.S. Pat. No. 4,558395 and 665,548, now U.S. Pat. No. 4,644,385, it has been proposed to provide a cooling structure for cooling a multichip module comprising a plurality of integrated circuit chips mounted on a single wiring substrate.
In the proposed cooling structure, a plurality of cooling blocks, connected by flexible pipes, are secured to or brought into contact with the respective individual integrated circuit chips, so that cooling efficiency can be greatly improved. From the aspect of maintenance and reliability, it is desirable to bring each of the cooling blocks into contact with the associated integrated circuit chip instead of securing the cooling block to the integrated circuit chip. When the cooling block is brought into contact with the associated integrated circuit chip, it is important, for the reduction of the thermal resistance, that the clearance between the opposing contact surfaces of the cooling block and integrated circuit chip be as small as possible. However, because of the manufacturing process, a warp of several .mu.m or more inevitably remains on these contact surfaces, especially, on the contact surface of the integrated circuit chip, and this warping has restricted the desired reduction in lower limit of the clearance between the opposing contact surfaces of the cooling block and integrated circuit chip, hence, the lower limit of the thermal resistance.
In view of the future tendency toward a larger size of integrated circuit chips and a more complicated multilayer interconnections, the warping of the integrated circuit chip is expected to increase.
Therefore, for a further improvement of the cooling efficiency, a cooling structure is required which can correct the undesirable warping of the contact surface of the integrated circuit chip and which can further decrease the clearance between the opposing contact surfaces of the integrated circuit chip and cooling block.
In this connection, David B. Tuckerman and R. Fabian Pease proposed a new cooling structure in a paper entitled "Microcapillary Thermal Interface Technology for VLSI Package" in 1983 Symposium on VLSI Technology, Maui, Digest of Technical Papers pp. 60-61. According to their proposal, a cooling block formed with very small or minute grooves on its contact surface is brought into contact with an integrated circuit chip through a layer of silicone oil interposed between their contact surfaces. The principle of the proposed cooling structure is that undesirable warping of the integrated circuit chip is corrected by utilization of negative hydrostatic pressure produced by the capillary action of the minute grooves.
However, in the case of a multichip module in which it is necessary to secure a plurality of integrated circuit chips to a wiring substrate as by controlled collapse bonding (CCB), it is difficult to correct warping of the integrated circuit chips by utilization of the negative hydrostatic pressure.